Adsorptive cryopumping method and apparatus

ABSTRACT

Cryopumping method and apparatus in which two cryopump chambers containing adsorbent are successively cooled and used to evacuate a third chamber by cryopumping. The first chamber to be cooled is used to evacuate the second chamber when both of the pump chambers are out of communication with the third chamber and before the second chamber is cooled. Then the first chamber is put into communication with the third chamber after the first and third chambers are sealed from each other.

e States ae Thibault et al. [45] June 13, 1972 [54] ADSORPTIVECRYOPUMPING [56] References Cited METHOD AND APPARATUS UNITED STATESPATENTS [721 Invent: i -J i 3,490,247 1/1970 Wing ..62/555 5 25'" ggf ff D 3,335,550 8/1967 Stern ..ss/2os 3,371,499 3/1968 Hagenbad ..62/55.5[73] Assignee: L'Alr Liquide Societe Anonyme pour 3,387,767 6/1968 Hecht..4l7/48 LEtude et L'Exploitatlon des Pr Georges Claude, Paris, Franceprimary wm y Wye 221 Filed: July 16, 1970 Attorneyg & Thompson [21]Appl. No.: 55,482 [57] ABSTRACT Cryopumping method and apparatus inwhich two cryopump [30] Foreign Apphcauon Priority Data chamberscontaining adsorbent are successively cooled and Dec. 1, 1969 France..6941309 u ed to evacuate a third chamber by cryopumping. The firstchamber to be cooled is used to evacuate the second chamber [52] US. Cl...62/55.5, 417/48, 417/901, when both f the pump chambers are out fcommunication 51 I CI 55/208 62/ with the third chamber and before thesecond chamber is cooled. T-hen the chamber is put into communicationthe third chamber after the first and third chambers are sealedADSORPTIVE CRYOPUMPING METHOD AND APPARATUS The present inventionconcerns a method and apparatus for pumping by adsorption, moreparticularly of the type in which a vacuum is produced in a chamber byplacing the chamber in communication with a body of adsorbent that hasbeen cooled to a very low temperature, e.g., cryopumping."

It is an object of the present invention to provide cryopumping methodsand apparatus that conserve the cryogenic liquid used for cooling.

Another object of the present invention is the provision of such methodsand apparatus that have reduced risk of contamination.

Still a further object of the present invention is the provision ofcryopumping methods and apparatus in which the apparatus can bestationary and relatively free from vibration.

Still another object of the present invention is the provision ofcryopumping methods and apparatus characterized by high thermalefficiency, high adsorptive capacity and improved heat transfer whilemaintaining a relatively small volume of the apparatus.

Still another object of the present invention is the provision ofcryopumping apparatus which will be relatively simple and inexpensive tomanufacture, easy to install, operate, maintain and repair, and ruggedand durable in use.

Finally, it is an object of the present invention to provide cryopumpingmethods which will be simple and reliable to produce relatively highvacuum for a given cost of operation.

Briefly, the objects of the present invention are achieved by providingtwo chambers containing adsorbent, by cooling a first of these chambers,by putting the chambers in communication with each other so that thecold first chamber adsorbs gases from the relatively warm secondchamber, by then cooling the second chamber by immersion in a cryogenicliquid while using the first chamber to cryopump gas from a thirdchamber which is the chamber to be evacuated, and finally by thereafterplacing the cooled second chamber in communication with the thirdchamber to further evacuate the third chamber while sealing the firstand third chambers from each other.

Other objects, features and advantages of the present invention willbecome apparent from a consideration of the following description, takenin connection with the accompanying drawings, in which:

FIG, 1 is aside cross-sectional view, somewhat schematic in nature, ofapparatus according to the present invention; and

FIG. 2 is a section taken on the line 2-2 of FIG. 1 and looking in thedirection of the arrows.

Referring now to the drawings in greater detail, there is showncryopumping apparatus according to the present invention, comprising avessel 40 having a bottom 41 and side walls 42 that are insulated and aninsulated cover 43 which may be releasably clamped on to close thevessel.

Disposed inside vessel 40 are several chambers. Chamber 44 is in theform of a bell and has an insulated top wall 45 and a cylindrical sidewall 46, which is also the radially inner side wall of a pumping chamber51 that is annular and that surrounds chamber 44. Chamber 51 also has acylindrical outer side wall 52, a bottom wall 53 and a top wall 54.Chamber 51 comprises a first cryopumping chamber.

Disposed within chamber 44 is a second cryopumping chamber 62 which issurrounded by but sealed from communication with and generally spacedfrom the side walls of chamber 44. Chamber 62 contains an uprightannular space 63 that communicates through an upwardly convergingconeshaped space 64 with an upright conduit 65 that is closed at itsupper end by an electrically operated valve 66. Disposed within chamber62 is a quantity of conventional cryopumping adsorbent 67 such as any ofa number of zeolites well known to persons having ordinary skill in thisart, which accordingly need not be further described. The adsorbent 67is disposed between a highly heat-conductive inner wall 68 of chamber62, which may be of copper or the like, and a screen 69 that radiallyoutwardly confines adsorbent 67 but exposes it to space 63. UprightU-shaped fins 80 of copper or the like are secured to wall 68 andpromote heat transfer between wall 68 and adsorbent 67 (see FIG. 2). Aradially outer side wall 70 completes chamber 62.

The portions of chamber 44 that are inside and outside the downwardlyopen bell thus fomied by chamber 62 communicate with each other throughan opening 48 through space 64.

Chamber 44 outside chamber 62 communicates with the outside of theapparatus through an upright conduit 72 controlled by a valve 73. Theinterior of chamber 44 outside chamber 62 also communicates with theinterior of vessel 40 through an opening 39 at the bottom of chamber 44.When valve 73 is closed, chamber 44 is closed except for opening 39.

Chamber 51 is filled with a cryogenic adsorbent 61 such as the zeolitementioned above, which communicates with the exterior of chamber 51 onlythrough an upright conduit 57 that may be selectively closed by anelectrically-operated valve 58. Valves 58 and 66 thus control thecommunication with a conduit 59 selectively closed by valve 60 andcommunicating with a third chamber to be evacuated (not shown).

The interior of vessel 40 outside chambers 51 and 44, which willhereinafter be called chamber 47, is adapted to be filled with acryogenic liquid such as liquid nitrogen 79, up to an initial level N,through an inlet 71. The liquid nitrogen 79 initially fills chamber 47to the level N but does not enter chamber 44 because valve 73 is closedand there is accordingly no way for the gas inside chamber 44 to escape.As initially filled, therefore, chamber 44 will contain no cryogenicliquid but chamber 47 will be filled to level N.

The first chamber 51 is traversed by a plurality of upright tubes 56open at both ends and having radially outwardly extending heat exchangediscs 38 thereon that penetrate adsor bent 61 to promote heat exchangebetween adsorbent 61 and tubes 56. Cryogenic liquid fills the tubes 56and abstracts heat from the adsorbent 61 by this heat exchange.

To effect desorption after the adsorptive cryopumping is completed, thecryogenic liquid is drained from the apparatus through a drain (notshown) so that the apparatus is entirely dry, and then the chambers 51and 62 are heated to desorb the adsorbed material, which leaves thechambers through conduits 57 and 65, respectively, valves 58 and 66being open, and is withdrawn from conduit 59 through a discharge conduit(not shown), the valve 60 being closed. To this end, an electricresistance heater 74 is provided under the bottom wall 77 of chamber 44,which also extends to some extent under chamber 51; and heater 74 isheated by electric resistance heating, the power being brought inthrough a cable 75 that traverses a tube 55 in one of the tubes 56 andthat leaves the apparatus through conduit 71.

In operation, with valves 60 and 73 closed, liquid nitrogen or othercryogenic liquid is supplied through conduit 71 into chamber 47 up tothe level N. As valve 73 is closed, substantially none of this liquidenters chamber 44 through opening 39. Therefore, first chamber 51 iscooled but second chamber 62 remains relatively warm. Valves 58 and 66are open, so that adsorbent 61 in chamber 51 tends to adsorb gas fromchamber 62; but of course no gas is withdrawn from the third chamber tobe evacuated, because valve 60 is closed.

When chamber 62 is thus purged of gas, valve 66 is closed and with valve58 remaining open, valve 60 is also opened. This seals off secondchamber 62 and places first chamber 51 directly in communication withthe third chamber to be evacuated. The relatively cold adsorbent 61 inchamber 51 adsorptively cryopumps a great deal of the gas out of thethird chamber.

In the meantime, the valve 73 is opened, which permits chamber 44 toflood with cryogenic liquid, the level of this liquid in chamber 47falling from N to N but remaining above the top of first chamber 51. Theliquid never enters chamber 62, because chamber 62 is sealed exceptthrough conduit 65; but the liquid surrounding and particularly theliquid inside the confines of the annular chamber 62 quickly abstractsheat from adsorbent 67 until this adsorbent is cooled to efficientcryoadsorption temperatures.

Then the valve 58 is closed, sealing off the used adsorbent 61 inchamber 51 and valve 66 is opened, placing second chamber 62 incommunication with the third chamber which is thus further evacuated bycryopumping from second chamber 62. The pressure in this third chamberis still further reduced by adsorption of most of its remaining gas ontothe adsorbent 67, it being remembered that this adsorbent 67 had beenpreviously desorbed by communication with adsorbent 61 before anycryopumping from the third chamber began.

When the pressure in the third chamber has thus fallen to its desiredvery low level, of the order of magnitude of mm. of mercury or evenless, then valve 60 is closed. It is now time to regenerate theadsorbents 61 and 67 by desorption; and to this end, the cryogenicliquid is drained from vessel 40 until the vessel is dry and then heater74 is energized so that the temperature of adsorbent 61 and 67 rises andgas is desorbed therefrom. This gas leaves through conduits 57 and 65and through open valves 58 and 66, valve 60 remaining closed, thedesorbed gas being removed from conduit 59 through an outlet opening(not shown). Of course, if the third chamber has been detached from theequipment, then the desorbed gas can be vented through open valve 60.

From a consideration of the foregoing disclosure, therefore, it will beevident that all of the initially recited objects of the presentinvention have been achieved.

Although the present invention has been described and illustrated inconnection with a preferred embodiment, it is to be understood thatmodifications and variations may be resorted to without departing fromthe spirit of the invention, as those skilled in this art will readilyunderstand. Such modifications and variations are considered to bewithin the purview and scope of the present invention as defined by theappended claims.

Having described our invention, we claim:

1. A method of cryopumping, comprising establishing first and secondchambers containing adsorbent, cooling the first chamber whilemaintaining the second chamber at a higher temperature than the firstchamber and maintaining the first and second chambers in fluidcommunication with each other thereby to cryopump gas from the secondchamber to the first chamber, thereafter sealing off the first andsecond chambers from each other and cooling the second chamber,establishing fluid communication between the first chamber and a thirdchamber to be evacuated, thereby to cryopump gas from the third chamberto the first chamber, and thereafter sealing off the first and thirdchambers from each other and establishing fluid communication betweenthe second and third chambers thereby to cryopump further gas from thethird chamber to the second chamber.

2. A method as claimed in claim 1, in which said cooling of said firstchamber while maintaining said second chamber at a higher temperature iseffected by immersing said first chamber in a cold liquid whilemaintaining said second chamber out of said cold liquid, and saidcooling of said second chamber is effected by immersing said secondchamber in the same liquid which previously cooled the first chamber.

3. A method as claimed in claim 2, in which the second chamber is firstmaintained out of the liquid and then immersed in the liquid bymaintaining and then releasing a body of confined gas about said secondchamber which when released escapes and permits entry of the liquidabout the second chamber,

4. Cryopumping apparatus comprising a vessel, a pair of chambers in saidvessel, each of said chambers containing adsorbent material, means forplacing said chambers in fluid communication with each other, means forselectively individually placing said chambers in fluid communicationwith a third chamber to be evacuated, means for admitting a cryogenicliquid into said vessel to surround said pair of chambers, and means forcontacting one of said pair of chambers with said liquid whilemaintaining the other of said pair of chambers out of contact with saidliquid, and for thereafter admitting said liquid into contact with saidother ofsaid pair of chambers, thereby selectively to cool first saidone and then said other of said pair of chambers.

5. Apparatus as claimed in claim 4, said admitting means comprisingmeans for selectively maintaining and releasing a body of confined gassurrounding said other chamber.

6. Cryopumping apparatus comprising a vessel, a plurality of pumpingchambers in said vessel each containing an adsorbent material, means foradmitting a cryogenic liquid into said vessel, means for thermaltransfer between the liquid and the adsorbent material in each saidchamber, means for bringing said liquid into contact successively withsaid thermal transfer means associated with each said chamber, means forindividually placing said chambers in fluid communication with anexternal chamber to be evacuated, and warming means for regeneratingsaid adsorbent material.

7. Cryopumping apparatus comprising a vessel, means for admitting acryogenic liquid into said vessel, a plurality of pumping chambers insaid vessel, each of said pumping chambers containing adsorbentmaterial, individual ducts extending from said chambers to the outsideof said apparatus, valve means in each of said ducts, a downwardlyopening bell in said vessel, one of said chambers being disposed in saidbell, said bell having a duct extending from the top of the bell to theoutside of the vessel, and a valve in the last-named duct forselectively maintaining and releasing a body of confined gas under saidbell thereby selectively to permit or prevent contact between said onechamber and said cryogenic liquid.

8. Apparatus as claimed in claim 7, said chambers being concentricallydisposed one within another.

9. Apparatus as claimed in claim 6, one of said chambers being annularand concentrically surrounding another of said chambers, said anotherchamber having a top wall, a cylindrical side wall adjacent said firstchamber, and heater means disposed below said another chamber forthermally regenerating said adsorbent.

10. Apparatus as claimed in claim 6, said thermal transfer meanscomprising tubes with fins extending inside the adsorbent, said tubesbeing open at both ends inside said vessel for the admission of saidcryogenic liquid.

1. A method of cryopumping, comprising establishing first and secondchambers containing adsorbent, cooling the first chamber whilemaintaining the second chamber at a higher temperature than the firstchamber and maintaining the first and second chambers in fluidcommunication with each other thereby to cryopump gas from the secondchamber to the first chamber, thereafter sealing off the first andsecond chambers from each other and cooling the second chamber,establishing fluid communication between the first chambEr and a thirdchamber to be evacuated, thereby to cryopump gas from the third chamberto the first chamber, and thereafter sealing off the first and thirdchambers from each other and establishing fluid communication betweenthe second and third chambers thereby to cryopump further gas from thethird chamber to the second chamber.
 2. A method as claimed in claim 1,in which said cooling of said first chamber while maintaining saidsecond chamber at a higher temperature is effected by immersing saidfirst chamber in a cold liquid while maintaining said second chamber outof said cold liquid, and said cooling of said second chamber is effectedby immersing said second chamber in the same liquid which previouslycooled the first chamber.
 3. A method as claimed in claim 2, in whichthe second chamber is first maintained out of the liquid and thenimmersed in the liquid by maintaining and then releasing a body ofconfined gas about said second chamber which when released escapes andpermits entry of the liquid about the second chamber.
 4. Cryopumpingapparatus comprising a vessel, a pair of chambers in said vessel, eachof said chambers containing adsorbent material, means for placing saidchambers in fluid communication with each other, means for selectivelyindividually placing said chambers in fluid communication with a thirdchamber to be evacuated, means for admitting a cryogenic liquid intosaid vessel to surround said pair of chambers, and means for contactingone of said pair of chambers with said liquid while maintaining theother of said pair of chambers out of contact with said liquid, and forthereafter admitting said liquid into contact with said other of saidpair of chambers, thereby selectively to cool first said one and thensaid other of said pair of chambers.
 5. Apparatus as claimed in claim 4,said admitting means comprising means for selectively maintaining andreleasing a body of confined gas surrounding said other chamber. 6.Cryopumping apparatus comprising a vessel, a plurality of pumpingchambers in said vessel each containing an adsorbent material, means foradmitting a cryogenic liquid into said vessel, means for thermaltransfer between the liquid and the adsorbent material in each saidchamber, means for bringing said liquid into contact successively withsaid thermal transfer means associated with each said chamber, means forindividually placing said chambers in fluid communication with anexternal chamber to be evacuated, and warming means for regeneratingsaid adsorbent material.
 7. Cryopumping apparatus comprising a vessel,means for admitting a cryogenic liquid into said vessel, a plurality ofpumping chambers in said vessel, each of said pumping chamberscontaining adsorbent material, individual ducts extending from saidchambers to the outside of said apparatus, valve means in each of saidducts, a downwardly opening bell in said vessel, one of said chambersbeing disposed in said bell, said bell having a duct extending from thetop of the bell to the outside of the vessel, and a valve in thelast-named duct for selectively maintaining and releasing a body ofconfined gas under said bell thereby selectively to permit or preventcontact between said one chamber and said cryogenic liquid.
 8. Apparatusas claimed in claim 7, said chambers being concentrically disposed onewithin another.
 9. Apparatus as claimed in claim 6, one of said chambersbeing annular and concentrically surrounding another of said chambers,said another chamber having a top wall, a cylindrical side wall adjacentsaid first chamber, and heater means disposed below said another chamberfor thermally regenerating said adsorbent.
 10. Apparatus as claimed inclaim 6, said thermal transfer means comprising tubes with finsextending inside the adsorbent, said tubes being open at both endsinside said vessel for the admission of said cryogenic liquid.